Posts Tagged ‘wheat pests’

Field Corn
We just received word from EPA that they did approve Delaware’s Section 18 emergency use request for Avipel® Hopper Box (dry) Corn Seed Treatment for the protection of field corn seed from consumption by black bird and crows. The effective dates of the Section 18 are April 20, 2011 – April 18, 2012. You can access the label on line at http://www.arkionls.com/. Producers are required to have a copy of the label in their possession to use the product. It is anticipated that product will be in the area this week for use by producers.

Wheat
This week we have had a number of calls about stink bugs and their impact on wheat. Some feel numbers are higher than normal and others think it is a typical year. In general, only a few brown marmorated stink bugs (Halyomorpha halys) have been found with the predominant species being native brown stink bug (Euschistus servus). In years past, we have seen brown stink bugs in wheat. After talking with entomologists in the region, we all feel that more work needs to be done to see if there is an impact from the boot through dough stages. Unfortunately, little is known about the impact of stink bugs on wheat on our area. In VA and North Carolina they feel they are seeing more each spring — mostly native browns but they also feel that wheat could become an early host for brown marmorated (BMSB). Our colleagues at the University of Maryland ( Cerruti Hook and Galen Dively) currently have replicated plots established and will be looking at the impact of BMSB on wheat, so we will know a lot more after the 2011 season. There is information on the internet from states to our south (Mississippi and Arknsas); however, at this point we do not know if that information applies to our area and much of the work was done in the 1980s. One of the concerns we have had is the ability of both species to move from wheat into corn and soybeans fields and this is one of the projects we in Delaware will be working on in 2011.

Alfalfa
Alfalfa Weevil: We are starting to see the first hatch of alfalfa weevil eggs. As soon as the weather begins to warm up, you should begin to sample for larvae on a weekly basis. Look for small larvae feeding in the tips of plants producing a round, pinhole type of feeding. Once you detect tip feeding, a full field sample should be taken. The most accurate way to time an application is to sample stems and determine the number of weevils per stem. A minimum of 30 stems should be collected per field and placed top first in a bucket to dislodge larvae from the tips. Then count the number of weevils per stem. The following thresholds, based on the height of the alfalfa, should be used as a guideline when making a treatment decision: up to 11 inches tall – 0.7 per stem; 12 inches tall – 1.0 per stem; 13 – 15 inches tall – 1.5 per stem; 16 inches tall – 2.0 per stem; and 17 – 18 inches tall – 2.5 per stem. Numerous pyrethroids are now labeled for alfalfa weevil including Baythroid XL, Mustang MAX, Proaxis, Warrior II and numerous generic pyrethroids. Imidan, Lorsban, Lannate and Steward are also labeled for alfalfa weevil control. Be sure to check all labels for rates, restrictions and days to harvest before application. The following is a link to our recently updated fact sheet including pictures of life stages and damage. http://ag.udel.edu/extension/IPM/ExtensionFactSheets/AlphalfaWeevilIPM-1.pdf.

Timothy
Cereal Rust Mites: Since spring green-up is underway, be sure to sample fields for cereal rust mite activity. Mites can be found in fields at this time. These mites are very small, so the use of a 20x-magnifying lens may be helpful. If rust mites become a problem, Sevin XLR Plus is still the only labeled, effective material: http://www.cdms.net/LDat/ld332013.pdf . Be sure to read the label for information on the number of applications per season as well as the days to harvest. For effective rust mite control, the use of the higher labeled rate and at least 25 gal/A of carrier to get good coverage of leaf surfaces generally results in better control. The following is a link to new fact sheet including pictures of mites and damage: http://ag.udel.edu/extension/IPM/ExtensionFactSheets/CerealRustMiteIPM-9.pdf.

Wheat
Cereal Leaf Beetle: It is time to begin sampling fields for cereal leaf beetle activity. We are starting to find evidence of adult feeding, so fields should now be scouted for egg masses. The threshold for cereal leaf beetle includes sampling for eggs, especially in high management wheat fields or in fields with historical problems. The eggs are elliptical, about 1/32 inch long, yellow in color when first laid, changing to a burnt orange prior to hatching. The following is a link to our recently updated fact sheet including pictures of life stages and damage: http://ag.udel.edu/extension/IPM/ExtensionFactSheets/CerealLeafBeetleFactSheetIPM-5.pdf.

Generally, eggs are laid singly or in small scattered groups (end-to-end) on the upper leaf surface and parallel to the leaf veins. Cereal leaf beetle larvae are brown to black, range in size from 1/32 to ¼ inch long, and eat streaks of tissue from the upper leaf surface. Since cereal leaf beetle populations are often unevenly distributed within the field, it is important to carefully sample fields so that you do not over or under estimate a potential problem. Eggs and small larvae should be sampled by examining 10 tillers from 10 evenly spaced locations in the field while avoiding field edges. This will result in 100 tillers (stems) per field being examined. Eggs and larvae may be found on leaves near the ground so careful examination is critical. You should also check stems at random while walking through a major portion of the field and sampling 100 stems. The treatment threshold is 25 or more eggs and/or small larvae per 100 tillers. If you are using this threshold, it is important that you wait until at least 50% are in the larval stage (i.e. after 50% egg hatch).

Winter Grain Mites: With the recent cooler weather, consultants are starting to report an increase in winter grain mite populations, especially in no-till wheat planted into corn stubble. Temperature and moisture are the most important factors influencing mite development and abundance. Cool, rather than warm, temperatures favor their development. Egg laying is heaviest between 50° and 60°F and the optimum conditions for hatching are between 44° and 55°F. Mite activity in the spring drops rapidly and the eggs fail to hatch when the daily temperature exceeds 75°F. The larvae as well as the adults feed higher up on the plants at night or on cloudy days. Heavily infested fields appear grayish or silvery, a result of the removal of plant chlorophyll by mite feeding. When high infestations feed on the plants for several days, the tips of the leaves exhibit a scorched appearance and then turn brown, and the entire plant may die. These mites do not cause the yellowing characteristic of spider mite feeding. Many of the infested plants do not die, but become stunted and produce little forage or grain; damage on young plants, however, is more severe than on large, healthy ones. Damage may also be greater in plants stressed by nutrient deficiencies or drought conditions. There are two types of damage to the small grain: (a) reduced amount of forage throughout the winter and (b) reduced yields of grain in the spring and summer. The following is a link to our recently updated fact sheet including pictures of mites: http://ag.udel.edu/extension/IPM/ExtensionFactSheets/WinterGrainMitesIPM-8.pdf.

The most effective scouting method is to use a 10x hand lens, checking both plant foliage and crop residue on the soil surface for the presence of immature and adult mites. A sweep net may also be effective in determining if mites are present. The best time to scout is early in the morning and at dusk on calm days because the mites will seek refuge during the day in the top 4 or 5 inches of the soil profile to avoid the sunlight. On cool, overcast days, they may be observed actively feeding on plant foliage throughout the day.

No economic thresholds have been developed for WGM in small grain fields. However, as a general rule of thumb, if plants exhibit symptoms of damage, weather conditions are favorable and several mites per plant are found, a chemical control may be necessary to prevent or reduce yield loss. If populations are small and the plants show no feeding injury or if populations and damage symptoms are isolated, the field should be scouted more frequently to insure yield losses are kept at a minimum.

Each year economic levels of true armyworm and grass sawfly can be found in fields throughout the state. Field scouting is the only way to determine if economic levels are present in your fields. The following information is a review of the biology and life history of grass sawfly and true armyworm in wheat.

Grass sawfly adults emerge in early April and begin to lay eggs in the leaf margins of small grains. Most egg-laying is complete by early May. The first larvae can be found by late April feeding on the lower leaf blades. Mature larvae can be distinguished by their solid green color, amber head with a brown band and many legs. Larval development takes approximately 21-30 days. By mid-June, larvae burrow into the ground and begin a period of summer diapause (hibernation). Sawfly larvae prefer to feed on the stems and are potentially more damaging than armyworms. Larvae begin to climb and feed on stems when the larvae are half grown and the grain is in the tiller to head stage. Stem clipping often occurs before leaf feeding is complete and/or the grain reaches physiological maturity. Head clipping often peaks before peak armyworm damage. (more…)

In recent years, we have had fewer problems with cereal leaf beetle due to a combination of good biological control programs and spring and summer weather conditions. However, each year we still have fields with economic damage so you still need to scout your fields in the spring as the cereal leaf beetle larvae can cause heavy damage and crop losses if not controlled when present.

As temperatures increase in spring (April normally), we begin to see adult cereal leaf beetles, especially along field edges that border woods or in protected areas. Adult beetles feed along the veins of grain leaves leaving characteristic narrow linear holes parallel to the leaf veins. Although they do not cause much damage, you should routinely check these areas since this is where you are likely to find the first eggs and larvae. Larvae can feed heavily on leaves, especially flag leaves, and can quickly cause significant yield reductions if they exceed the economic threshold level. (more…)

We are starting to receive questions regarding the need to spray for aphids in late winter and early spring in regards to both barley yellow dwarf virus (BYDV) transmission and direct aphid damage. Although fall conditions were favorable for aphids (warm and dry), we did not see an increase in populations in many wheat fields until late November and early December. In addition, there have been reports of a second period of population increase in late January and early February.

All of the aphids found in Delaware wheat fields are capable of transmitting BYDV. However, the virus strains that cause barley yellow dwarf are generally transmitted to the wheat in the fall or early spring before growth stage 4. For aphids to successfully transmit the virus in the most efficient manner, they normally need between 12 and 30 hours feeding to acquire the virus, and then 4 or more hours of feeding to transmit it. However, aphids are capable of acquiring the virus after feeding on infected plants for only 30 minutes. Once they acquire the virus and it is allowed to incubate for one to four days, they can transmit it to healthy plants for the rest of their life. (more…)

A number of fields were sprayed for winter grain mites in Virginia in late December and early January. In early February, a number of fields were also sprayed on the eastern shore of Maryland. Although we are now past the first generation, a second generation in March and April could cause additional damage. The following is an overview of this pest including pest identification, biology/life history and management options written by Dr. Ames Herbert from Virginia Tech.

“Winter grain mites attack small grains, including wheat, barley, and oats. Other hosts include grasses, especially bluegrass, bentgrass, ryegrass, and fescue. The mite also infests and damages legumes, vegetables, ornamental flowers, cotton, peanuts, and various weeds. Adult mites are about 1 mm long, black, with red legs and are fast moving. They quickly run to ground cover when you approach plants. As the name implies, they are winter pests. There are two generations per year. The first develops from over-summering eggs. Development begins after the onset of favorable temperature and moisture conditions in late September and October with populations peaking in December and January. The second generation develops from eggs laid by the first generation reaching maximum infestation density in March and April. Populations then decrease as temperatures exceed the range of tolerance. The females of this generation lay aestivating or over-summering eggs. (more…)

Last fall, we received a number of calls regarding the need to control Hessian fly in wheat. Although we have not seen or heard of any significant damage from fall infestations, we continue to receive questions about the possibility of problems from the spring population. If stands appear thin and you are checking fields for a reason, you should consider Hessian fly as one of the possible culprits. Volunteer wheat could also be a source of spring infestations. Although the adult fly is not a strong flyer, production fields near volunteer fields that were heavily infested last fall could be at risk for a spring infestation. When the Hessian fly adults emerge from the flaxseed this spring they will seek a host upon which to lay their eggs. Wheat is the principal host plant of the Hessian fly but it may also be found on rye, barley and other wheat-related species.

Although we have not had experience controlling spring infestations with a foliar insecticide, information from North Carolina and Georgia indicated that it can be done but it will not be easy to time applications. Information from North Carolina indicates that if applied timely, Warrior® will provide control. (See link to North Carolina publication). (more…)